【作者】 黄川徽；

【导师】 徐铜文；

【作者基本信息】 中国科学技术大学 ， 应用化学， 2008， 博士

【摘要】 利用有机胺吸收脱除烟气或者燃气中的二氧化硫是当前较为成熟也是应用较为广泛的脱硫技术之一,该技术利用有机胺与二氧化硫形成热不稳定性盐的特性加热来再生脱硫剂和回收二氧化硫,但是在硫吸收和有机胺脱硫剂再生过程中会由于含硫气体和亚硫酸胺盐的氧化形成了热稳定性盐——胺硫酸盐,影响脱硫效率和热再生效率。由于这种热稳定盐在在循环过程中的不断积累,一方面,会直接导致有机胺的损失、降低脱硫效率,增加有机胺原料成本;如果不能循环利用而被排放到环境中去,这些热稳定性盐不仅会造成二次污染而且还会导致资源的浪费。另一方面,会导致流体粘度增加,进而造成鼓泡、液泛,影响操作的稳定性,严重者会直接导致脱硫操作的停车。因此不论从经济成本角度还是从环境保护角度,脱硫工艺亟须与绿色/环境化工技术耦合实现没有二次污染的大气污染治理新工艺。双极膜电渗析技术可以参与这一耦合过程,因为热稳定性盐可以在双极膜电渗析中解离并与双极膜水解离产生的OH^-和H⁺结合转化为有机胺和硫酸。在线耦合以后,双极膜电渗析可以及时回收热稳定性盐中的有机胺,确保脱硫体系高效稳定长期运行;而且双极膜电渗析以水和热稳定性盐为主要反应试剂、使用的支撑电解质可以循环利用,因此没有二次污染问题。本论文以双极膜电渗析再生有机胺脱硫剂为切入点,探讨了电膜技术对脱硫工艺的绿色化和环境友好化的共性问题,研究内容和主要的结果如下:1.选取一种高效有机胺排烟脱硫剂——哌嗪,采用双极膜电渗析对其硫酸盐进行再生,探讨工艺可行性,并且考察电解质浓度、料液浓度、电流密度、膜堆构型对再生效果的影响。结果显示低能耗高电流效率对应的操作条件为c₀（Na₂SO₄）=0.3～0.4 mol/L,c₀（Pz·H₂SO₄）=0.08～0.13 mol/L,以及采用BP-C-C（BP,双极膜;C,阳膜）构型;而且在高电流密度条件下操作电流效率和能耗都比较高。根据实验条件估计哌嗪再生的过程成本为0.96 $/kg Pz。为了提高电流效率,同离子渗漏往往作为不利因素而加以抑制。在本实验中这种同离子渗漏导致电流效率下降的现象也存在,但是对于BP-C-A（A,阳膜）构型膜堆来说一定量的H⁺渗漏对提高电流效率是有好处的,因为它可以在硫酸哌嗪缓冲容量范围内在不增加H⁺/PzH_nⁿ⁺比的情况下增加哌嗪离子PzH_nⁿ⁺的含量。从这个意义上说,在采用BP-C-A构型膜堆再生哌嗪时阴膜的离子选择性不必要求得过高。2.在同等条件下,选取和双极膜电渗析最有竞争力的常规电渗析实现上述有机胺硫酸盐的再生过程,并对再生性能和成本进行系统的比较。结果发现,常规电渗析具有较高的哌嗪产量和电流效率,以及较低的膜堆电压降和能耗。但是,其过程成本比双极膜电渗析高,原因在于常规电渗析在再生哌嗪过程中中需要额外支付碱和附属设备的成本。根据计算结果,两种技术再生哌嗪的过程成本估计为:双极膜电渗析,0.96 $/kg Pz;常规电渗析,1.14 $/kg Pz。3.选取三种有机胺燃气脱硫剂——单乙醇胺（MEA）、二乙醇胺（DEA）和和N,N’-二甲基乙醇胺（DMEA）,探讨双极膜电渗析再生这些脱硫剂硫酸盐的可行性,考察电解质浓度、料液浓度、电流密度、膜堆构型对再生效果的影响,并利用分子大小、本征迁移速率、离子浓度、Donnan渗析、离子取向和链烷醇胺与膜的相互作用解释了MEA、DEA和DMEA在再生性能上的差异。根据实验条件估计MEA、DEA和DMEA的再生过程成本分别为0.48、0.32和0.30 $/kg。4.将有机胺酸盐再生和葡萄糖酸生产过程在双极膜电渗析内部进行耦合,探讨其可行性,并考察料液浓度、电流密度对过程性能的影响,比较耦合操作和分离操作的优劣。结果显示耦合操作时哌嗪（Pz）再生和葡萄糖酸（HGlu）生产的过程成本分别为$0.80 kg^-1Pz和$0.17 kg^-1HGlu,比分离操作要低($0.96kg^-1Pz和$0.24 kg^-1HGlu)。该研究的意义在于借助正规模效应和投资平分减少单方投资实现合作企业间的双赢,从而集中弱小力量形成合力推动双极膜电渗析的工业化应用。本文研究结果表明,采用双极膜电渗析再生有机胺脱硫剂不仅是可行的,而且是经济有效的。鉴于双极膜电渗析的固有工业生态学特征,我们相信该技术必定为绿色/环境化工注入持久力量。更多还原

【Abstract】 Wet absorption using amines is a predominant technique employed to desulfurize flue-gas and fuel-gas since it can regenerate amines and recover SO₂ by heating heat-unstable amine sulfites.Nonetheless,heat stable salts form and accumulate in the recirculation because of the oxidation of sulfur dioxide or amine sulfites during absorption and regeneration.These heat stable salts cannot be regenerated by heating and will lead to a loss of amines,a decrease in desulfurizing efficiency,and an increase in chemical cost.If discharged without treatment,these salts will give rise to a second pollution and waste of resources. On the other hand,heat stale salts,if accumulated in the desulfurizing solution, will result in an increase in fluid viscosity and then a chain reaction:bubbling, flooding,and even shutdown.Therefore,whether from the viewpoint of process cost or environmental protection,it is necessary to couple current desulfurizing processes with green chemical techniques and achieve an air pollution control without second pollution.Electrodialysis with bipolar membranes（EDBM）is such green chemical technique because these heat stale salts can be converted to amines and sulfuric acid in EDBM.If coupled with current desulfurizing processes in situ,EDBM can regenerate amines timely and ensure a long-term,efficient,stale desulfurization. In addition,second pollution is eliminated since EDBM adopts water and heat stable salts as reactants and the supporting electrolyte used in the EDBM stack can be circulated in the corresponding cycle.Therefore,the application of EDBM to regeneration of amine desulfurizing agents becomes the focus of this research.The results and conclusions are as follows.A highly-efficient amine flue-gas desulfurizing agent—piperazine is chosen to test the feasibility of applying EDBM to regeneration of amines since it forms piperazine sulfate—a heat stale salt—in the process of SO₂ absorption.The factors considered include electrolyte concentration,piperazine sulfate concentration,current density,and stack configuration.The results indicate that the low energy consumption and high current efficiency are achieved when applying electrolyte solutions of middle concentration（c₀（Na₂SO₄）=0.3～0.4 mol/L）,piperazine sulfate solution of middle concentration （c₀（Pz.H₂SO₄）=0.08～0.13mol/L）,and EDBM stack of BP-C-C（BP,bipolar membrane;C,cation-exchange membrane）configuration.The results also indicate that when applying a high current density to the EDBM stack,it has a high current efficiency and energy consumption.The process cost is estimated to be 0.96$/kg Pz for regeneration of piperazine with the laboratory-scale experimental equipment.The co-ion flux is considered as an unfavorable factor for high current efficiency.However,a certain amount of H⁺ flux can improve the current efficiency in the case of the EDBM stack of BP-C-A（A,anion-exchange membrane）configuration because it increases the amount of PzH_nⁿ⁺ions in the salt compartment without an increase in H⁺/PzH_nⁿ⁺ratio in the buffering range of piperazine sulfate.In that sense,the ion selectivity of anion-selective membrane does not need to be too high when applied to regenerate piperazine by using a EDBM stack of BP-C-A configuration.Under identical conditions,a systematic comparison is made on the regeneration of piperazine by using EDBM and conventional electrodialysis（ED）: the latter is a competitive technique as compared with EDBM.ED has higher piperazine yield and current efficiency,and much lower voltage drop and energy consumption.However,its process cost is higher than that of EDBM due to an extra expenditure for the base and its tank and pumps.The process cost is estimated to be 0.96$/kg Pz for EDBM and 1.14$/kg Pz for ED.The feasibility is also tested on the application of EDBM to regeneration of three fuel-gas desulfurizing and decarbonizing agents:monoethanolamine（MEA）, diethanolamine（DEA）,and N,N’-dimethylethanolamine（DMEA）,which still form heat-stable salts—alkanolamine sulfates.The effects of operation parameters （electrolyte concentration,alkanolamine sulfate concentration,and current density） on regeneration are analyzed on the basis of ion dimensions and intrinsic transport velocities,ion concentration,Donnan dialysis,ion orientation,and the interaction between alkanolamines and membranes.The process cost is estimated to be 0.48, 0.32,and 0.30$/kg for MEA,DEA,and DMEA,respectively.To push EDBM to industrialization,a win-win process coupling is investigated in EDBM to simultaneously regenerate piperazine and produce gluconic acid.The feasibility of such coupling is verified after investigating the operation parameters（such as feed concentration,current density,and operation mode）.The process cost is estimated to be $0.80 kg^-1Pz and $0.17 kg^-1HGlu in the coupled operation,which are less than those in separate operations—$0.96 kg^-1Pz and $0.24 kg^-1HGlu.The purpose of this coupling is to achieve a win-win collaboration between enterprises via allocation of investment and economies of scale.As proven,EDBM is not only scientifically novel but also economically feasible and attractive besides its environmental benefits.In view of those properties characteristic of industrial ecology,EDBM will become one of the mainstays for the development of green and environmentally-friendly chemical industries.更多还原